An investigation of the role of the Drosophila zeste gene product in synapsis-dependent gene expression (transvection) is proposed. The experiments described will extend previous findings that this protein binds to specific DNA sequences and acts as a transcription factor in vitro and cotransfection assays. The approach outlined first requires detailed study of the organization of functional domains of the zeste protein. This information will then be used in the design of model systems to test specific hypotheses of its activities in transvection. Using deletions of zeste sequences, domains of zeste required for its nuclear localization, possible multimerization or contacts with other proteins, cooperative DNA binding, and transcriptional activation properties will be identified. This work will be supplemented by an analysis of altered zeste proteins encoded by mutations with known genetic properties. Information generated in this manner should add to understanding of the molecular basis of dominance relationships between zeste alleles and the differing requirements for target gene dosage in the manifestation of their mutant phenotypes. Identification of regions of the zeste protein involved in particular aspects of its function will be exploited to create chimeric proteins useful for the establishment of a model system for transvection. Trials in both yeast and Drosophila will be performed to test detailed hypotheses for the role of the zeste gene product in this phenomenon. Possibilities to be investigated include: (a) zeste mediates the looping and pairing of DNA sequences; (b) zeste function requires synergistic interactions with other transcription factors, (c) zeste functions in a manner similar to other transcription factors, but unique elements of its structure are required for transvection, and (d) cooperative binding of zeste subunits is central to its function in transvection.